With rapid development of information technique, the requirement for the power supply system increases. For some important electric equipment, such as communication equipment, if the power supply of the power supply system is suddenly interrupted, it is easy to lose some important data, and the normal operation of other relevant systems may even be affected, so as to bring a serious consequence. Thus, in order to avoid the above cases, besides a commercial power as a main power supply, other equipment such as a battery group is used as a backup power supply for some important electric equipment. Therefore, a certain requirement is proposed for the switch between the main/backup power supplies.
In the prior art, there are mainly three switch solutions described below.
The first solution: a power supply switch between the main/backup power supplies is implemented by switching a movable contact of the relay between a first movable contact and a second movable contact and connecting a bulk capacitor to the load side, as specifically shown in FIG. 1. In this way, a smooth switch between the main/backup power supplies is implemented, and an energy storage function of the backup power supply is fully exerted. However, there are some disadvantages as following.
1. There is a large fluctuation of the voltage of the load, and the switch between the main/backup power supplies will cause some phenomenon such as the powerdown when the voltage of the backup power supply is low.
2. The capacitor is charged rapidly at the moment when connecting with the power supply system, such that the circuits in front of the capacitor are easily to be damaged. Therefore, the bulk capacitor is easy to introduce a hidden danger in the circuit and the cost is increased. However, the main/backup power supplies cannot be switched smoothly without the bulk capacitor storing the energy.
The second solution: a diode is used to implement the power supply switch between the main/backup power supplies, as specifically shown in FIG. 2. In this way, a smooth switch between the main/backup power supplies can be implemented without a bulk capacitor for performing an auxiliary switch. However, there are some disadvantages as following.
1. A large voltage drop will be generated at the PN junction of the diode when a large current flows through the diode, and thus the energy storage function of the backup power supply cannot be fully exerted.
2. A large amount of power consumption will be generated at the diode, and thus the reliability of the operation of the circuit will be ensured by a radiator used for heat dissipation. Meanwhile, a largely increased temperature will cause a performance degradation of devices around the diode and be adverse to miniaturize the product.
3. Since there is no over discharging protection function, the backup power supply still supplies power to the load even when the electric quantity thereof is not sufficient, such that the service life of the battery is decreased.
The third solution: a transistor is used to implement the power supply switch between the main/backup power supplies, as specifically shown in FIG. 3. Due to the short turn-on time of the transistor, a smooth switch between the main/backup power supplies is implemented. Moreover, the voltage drop of the transistor can be adjusted to be low, so the energy storage function of the backup power supply can be fully exerted. Meanwhile, a bulk capacitor is not needed for the auxiliary switch. However, there are some disadvantages as following.
1. The backup power supply is charged directly by the main power supply when a short circuit is caused due to a failure of one of the transistor Q1 and the transistor Q2, which will shorten the service life of the backup power supply and may cause the backup power supply bomb.
2. A large amount of power consumption will be generated at the transistors, and thus a radiator has to be used also. Meanwhile, a too high temperature will cause a performance degradation of devices around the transistor and be adverse to miniaturize the product.